Conventionally, different types of conductors are connected to each other in a wire harness that is to be mounted on, for example, a vehicle or the like. For example, Patent Document 1 below discloses that, in order to reduce the diameter of electrical wires in a wire harness, single-core wires, which have a small diameter, are used in a section that does not need to be flexible, twisted wires are used in a section that needs to be flexible, and single-core wires and twisted wires are connected to each other. A flat squashed portion is provided at an end of a single-core wire, and the squashed portion and the conductor of a twisted wire are connected to each other through ultrasonic welding.